1. Field of the Invention
This invention relates to an observation or measurement means and an observation or measurement system provided with this means, and more specifically, to a feeble light image pickup optical system capable of detecting feeble light from an object, such as radiation from a living body, and an microscope apparatus provided with this optical system, a microscope system provided with the microscope apparatus, and an observation apparatus capable of observing the interior of a living cell and an observation system provided with this observation apparatus.
2. Description of Related Art
In the most advanced research field at present, various methods of observing cells, in vivo, for a long period of time (several days to several weeks) are developed for purposes of the functional clarification of living cells and the behavior analysis and interaction clarification of a protein. As one technique of observation by an observation apparatus such as a microscope for observing a lesion part inside a living cell, the method of a fluorescence observation is largely used. The fluorescence observation is such that, after a particular fluorescent substance like a fluorescent protein is used as a light-emitting label to stain a living specimen like the living cell, fluorescent light is produced by irradiating the specimen with exciting light and is observed to thereby detect the existence of a particular part in the living specimen, such as the lesion part inside the living cell, and its position.
In conventional practice, observation apparatuses for observing living cells, including fluorescence observations, and optical systems used in the observation apparatuses are set forth, for example, in Japanese Patent Kokai Nos. Hei 5-113540, Hei 10-31162, Hei 11-231224, and 2001-21812.
The fluorescence observation, however, has problems described below.
In order to produce fluorescent light, it is necessary to increase the intensity of exciting light, to some degree, with which the living cell is irradiated. However, if the irradiation of high-intensity exciting light is continued, the living cell will suffer serious damage. In the fluorescence observation, therefore, it is difficult to observe the living cell in a stabilized condition for a long time. Since the living specimen is irradiated with the exciting light in the fluorescence observation, the background other than the fluorescence is increased and is liable to adversely affect an S/N ratio. As such, in the fluorescence observation, the quantification of fluorescence measurement becomes a problem. Furthermore, in the fluorescence observation, the fluorescent substance and the apparatus for carrying out the fluorescence observation are expensive and bring about high costs.
In recent years, however, it has been required to detect radiation from the living cell without irradiating the living cell with the exciting light and thereby to detect the existence of a particular part, such as the lesion part, inside the living cell, and its position.
In a method of detection with light emission, for example, a particular part or a functional protein in the living cell is labeled by a particular auto-luminous enzyme like a luciferase gene that is a bioluminescence enzyme, and its radiation is detected.
According to the method of detection with light emission, the irradiation of the living cell with the exciting light that formerly has been required for the fluorescence observation becomes unnecessary, and thus the fluorescence observation can be made in a stable condition for a long period of time without causing damage to the living cell. Moreover, it is possible to make measurements that the background becomes low, the S/N ratio is high, and the quantification is excellent.
On the other hand, in the method of detection with light emission, radiation from the luminous enzyme like the luciferase gene is low in intensity and faint, and hence there is the disadvantage that faint light must be detected.
Conventional optical apparatuses for detecting faint radiation are described, for example, in U.S. Pat. No. 6,754,008 B1 and Japanese Patent Publication No. Hei 1-45020.
In the fluorescence observation, as mentioned above, when the living specimen receives some stimulation in such a way that it is irradiated with the exciting light, there is the possibility that the stimulation itself adversely affects an active condition of the cell. Consequently, the observation system requires that a luminous label is stimulated by the lowest possible stimulation (low-intensity exciting light) so that a weak luminous signal produced in accordance with this stimulation can be detected at extremely high efficiency.
At the same time, the observation system also requires that provision is made so as not to lose a state of movement of the living cell and at the same time, information from many cells are detected at a time by observations in a wide range and a processing speed and work efficiency can be improved.
The observation system further requires having flexible extensiveness allowing a combination with another observation method and the interchangeability with a conventional observation system.
However, in the fields of the above conventional observation apparatuses set forth in Kokai Nos. Hei 5-113540, Hei 10-31162, Hei 11-231224, and 2001-21812, observation apparatuses and observation systems satisfying these requirements do not exist.
In the optical apparatus for detecting faint radiation, the above apparatus set forth in U.S. Pat. No. 6,754,008 B1 is such that its optical system is constructed as a demagnifying system. With the apparatus described here, therefore, faint radiation emanating from the particular part of the living cell cannot be detected.
The above apparatus set forth in Japanese Patent Publication No. Hei 1-45020 is provided for the purpose of measuring an aging expression level in the cell by using the luminous enzyme like the luciferase gene. In this apparatus, however, the average value of the entire cell on the analysis of the expression level is measured and the expression level of each cell cannot be obtained.
In order to use a conventional microscope to detect faint radiation, a costly photon counting system is required.